Integrated circuits are typically formed on a substrate such as a semiconductor wafer. Bonding bumps (bump-on-trace, or BOT) are part of the interconnecting structure in an integrated circuitry. A bump provides an interface to an integrated circuit device through which an electrical connection to the device may be made. Conventional techniques may be used to provide a connection from a package terminal to an integrated circuit using the thermocompression or thermosonic wire bonding and other techniques known in the art.
Chip interconnection techniques such as the flip chip, also known as Controlled Collapse Chip Connection or its acronym, C4, interconnect semiconductor devices to external circuitry with solder bumps that have been deposited onto the chip output contacts. The solder bumps are deposited on the chip pads on the top side of the wafer during the final wafer processing step. In order to mount the chip to external circuitry (e.g., a circuit board or another chip or wafer), the chip is flipped over so that its top side faces down, and its contacting pads overlay with matching pads on the external circuitry, and then the solder is flowed between the flipped chip and the substrate supporting the external circuitry to complete the interconnect. This is in contrast to wire bonding, in which the chip is mounted upright and wires are used to interconnect the chip pads to external circuitry. The resulting completed flip chip package is much smaller than a traditional carrier based system, because the chip sits right on the circuit board. When the interconnect wires are much shorter, the inductance and resistive heat are greatly reduced. Therefore, flip chip allows higher-speed devices.
BOT structures may sometimes suffer from peeling-off or delamination. For example, during processing, undercut regions may form on the traces. These undercut regions coupled with stress generated by a mismatch between the coefficient of thermal expansion (CTE) of the device die and the CTE of the package substrate may increase the likelihood of peeling-off or delamination in the resulting package.